There are numerous commercial/industrial applications for radio-transmitter combinations wherein frequency modulation is used to convey data. For example, small battery operated FM transmitters and permanently installed receivers are used to control security systems, automatic gate openers, automatic garage door operators and the like. There has been a significant trend toward the miniaturization of the circuitry in such devices as well as a push for increased economy and reliability through the use of integrated circuit technology.
Prior art FSK demodulator circuits have been primarily, if not exclusively, analog devices and the components of such circuits do not lend themselves to integrated circuit technology and implementation. Other receiver portions such as a signal decoder, on the other hand, are easily implemented using digital and integrated circuit technology. Accordingly, one might find a commercial receiver having a hybrid combination of analog and digital devices. Cost cutting, improved reliability and reduced size are among the principal objectives which can be realized by eliminating this hybrid arrangement in favor of all integrated circuit implementation.